The present invention relates to a processing method and to an apparatus for a rewritable card having a printing layer in which images such as characters and patterns can be printed by predetermined heating/cooling processes, and more specifically relates to a technology for improving erasing properties of images.
Recently, various kinds of magnetic cards are used for many purposes. Among these, there are types of cards on which changing information is updated and indicated on the card every time the card is used. As examples of such cards, prepaid cards such as telephone cards and train cards on which the balance is indicated, point cards in which points are added according to a purchase amount, and consultation appointment for dental clinics cards in which the next consultation day and time are indicate and the like may be mentioned. In the past, images of changing information were generally written on cards by a printer of the dot impact-type or the thermal-type. In these types of printing, however, all the printed images were remained and the history thereof was indicated, and therefore, it was necessary to make the images small or to enlarge the printing area to obtain the necessary number of printing lines. Therefore, there were problems in that printed images were not easy to read and the area for indicating permanent images such as patterns and names in addition to the variable information was narrow.
Recently, rewritable cards in which previous images are erased and only the newest images are printed at the same position as the previous images are available. Such a rewritable card is manufactured of a resin substrate and a rewritable layer which is made of a heat-reversible recording material and which is laminated on the substrate. A thermal head unit of a card processing apparatus performs heating/cooling processes on the rewritable layer according to the characteristics thereof so as to repeatedly perform erasing/printing, in other words, so as to rewrite images. The card processing apparatus is generally constructed to thrust erasing and printing heads heated to a printing layer of a card, thereby performing erasing/printing processes, while traveling the card which is clamped between the erasing head and a platen roller, and is subsequently clamped between the printing head and a platen roller.
In accordance with the inventors' research, the heat-reversible recording material has a property in which the temperature range for reaching the erasing condition (temperature at initiation of printing to temperature at initiation of erasing) changes according to the ambient temperature, in other words, the temperature of the card. In particular, it has been known that the temperature range becomes remarkably narrow when the ambient temperature is relatively low, for example, when it is lower than 15.degree. C. The reason for this is believed to be that at low temperatures, the difference between the temperature of the card and the temperature of the erasing head is large, and therefore the temperature gradient along the depth of the card in the conduction of heat from the erasing head to the printing layer is large, and that the card becomes hard, so that contact between the erasing head and the card is reduced. Therefore, erasing errors easily occur when the temperature is low, and the erasing properties are thereby degraded.
Resin substrates forming base elements of rewritable cards are formed of various materials such as PET (polyethylene terephthalate), which is flexible, and PVC (polyvinyl chloride) on which embossing is preferably performed, and these resins have differing hardnesses. In general, a printing layer is integrally formed by pressing a substrate. The surface of such a card has a form in which the center thereof in the width direction projects slightly. As a result, contacting properties of the erasing head with respect to the entire surface of the printing layer are degraded, so that images at both sides of the printing layer cannot be erased. The contacting properties are substantially degraded at low temperatures and in hardened cards, so that the entire width of the printing layer cannot be available, and the printing area is necessarily reduced.